In liquid purification systems, which involve various types of settling tanks, it is often necessary to remove impurities from the upper regions of the tank contained liquid, such as scum, floating debris, oil layers and the like. Removal of this upper layer may be accomplished by a variety of techniques including inducing liquid flow patterns which cause the upper layer of scum or foam to flow over a weir, mechanical moving rakes which are drawn across the liquid surface and by rotatable scum removing troughs. The scum removing trough is normally used in situations which require infrequent removal of scum and other floating debris and which are normally partially immersed in the contained liquid of the tank. Due to the infrequent use of a skimming trough, it is normally operated by hand by rotating the trough up to approximately 90.degree. which lowers the opening of the trough into the upper region of the contained liquid to remove adjacent debris and unwanted layers of liquid. The trough is rotated back to its upright position allowing the skimmed liquid and debris to flow out of the trough through an outlet at one end of the trough.
Examples of such trough skimmers are disclosed in U.S. Pat. Nos. 2,220,959, 2,337,859, 2,455,338 and 3,419,153. The significant problem with these skimming trough arrangements and with all other known skimming trough arrangements is the manner in which the trough ends or intermediate portions are mounted within the settling tanks. Due to the infrequent operation of the skimming troughs, it is thought that the simplest of bearing structures will do. However, it has been found that, in using such trough arrangements over extended times, such as five to ten years, the bearings seize and, therefore, require replacement. This seizure is usually caused by one metal surface abrading against another metal surface, such as the bearing arrangement disclosed in U.S. Pat. No. 3,419,153. In that arrangement, the bearing surfaces are provided by contacting metal structures of the bearing face and the trough. Such arrangements are very rigid and do not provide for flexibility in either axial movement and/or sloping of the trough. The tilting of the trough is necessary to ensure that skimmed liquid flows to the outlet end of the trough. Axial movement in the trough is usually induced by thermal expansion and contraction in the trough due to change in ambient temperature, since these devices are commonly used in the out of doors. The sealing arrangement is such that the bearing surfaces are exposed to the contained liquids. This can result in corroding of the bearing surfaces further adding to the seizing of the bearings.
Another difficulty with respect to sealing is that any water in the contained liquids, should it seep into the bearing arrangement, can freeze in cold temperatures. This precludes rotation of the trough to remove scum from the upper surface of the settling tank. This requires heating of the bearings to thaw them for use.